The present invention relates to a blood tube. More particularly this invention concerns an apparatus for forming a partial vacuum in a blood tube.
As described in U.S. Pat. No. 3,136,440 of A. Krug a standard blood tube, in which a sample of a patient""s blood is held after being drawn and before being subjected to whatever tests are required, is typically formed as a hard plastic or glass tubular vessel having a mouth sealed by an elastomeric membrane or plug. Such a blood tube is a disposable item that is mass produced.
When the tube is to be opened so that the blood can be tested, it is necessary to tear off the membrane or pull out the plug. This action typically creates a momentary superatmospheric pressure in the container so that any blood around the mouth can be expelled as an aerosol during the opening operation. Obviously this can be extremely dangerous for the person handling blood samples that may carry a deadly communicable disease.
It has been suggested to provide a special opening apparatus, but such machinery is complex, creates sterility problems in itself, and represents a bottleneck in the handling of blood samples in a laboratory. A system described in U.S. Pat. No. 4,036,387 of W. Feaster allows blood to be withdrawn from a filled sealed tube wholly by a device which protects the user, but this system is fairly complex and expensive.
Hence it has been suggested in German 2908817 of W. Feaster to depressurize, that is form a partial vacuum, in the tube after it is filled. In this manner, when the closure is removed, there will be a small flow of air into the tube, so that any drops of blood at the closure will not be expelled. Instead they will be sucked back in. In the system of DE 2908817 the blood-filled tube is oriented horizontally and a needle is pierced through its closure to suck out some of the air in the tube and produce the desired partial vacuum. Such a machine has the considerable problem that occasionally, particularly when the tube is quite full, that the air-aspirating needle can get contaminated. As a result infectious agents can be transferred from one sample to the next.
It is therefore an object of the present invention to provide an improved apparatus for forming a partial vacuum in a blood tube.
Another object is the provision of such an improved apparatus for forming a partial vacuum in a blood tube which overcomes the above-given disadvantages, that is which is simple and easy to use and which maintains sterility from one tube to the next.
A tube holding a sample of blood and having an end provided with a pierceable closure is partially evacuated of gas by an apparatus that has according to the invention a stationary guide defining an axis inclined at an angle to the horizontal. A needle fixed in the guide projects axially downward therein. A slide in the guide forms a downwardly inclined and open seat centered on the axis and adapted to receive the end of the tube. The slide is movable in the guide between an outer position with the seat spaced past an end of the needle and an inner use position with the needle projecting into the seat so that in the use position the needle projects through the closure of the tube fitted to the seat. The slide is urged axially downward in the guide, and a pump is provided for aspirating air through the needle.
Thus with this system the tube is never laid perfectly horizontal as in the above-described device, so that the blood in the tube is not in contact with the closure during the evacuating operation. Instead the tube is held at an angle by the evacuating apparatus so that when the needle pierces its closure, this needle will be out of contact with any fluid therein and will be able to withdraw gas from the tube until the desired subatmospheric pressure is established therein.
In accordance with the invention a spring is braced between the guide and the slide and constitutes the biasing means urging the slide downward. Furthermore according to the invention the tube is of such a length that, when fitted to the seat in the use position, it tube projects substantially from the slide.
Thus the device is simple to operate. All the user needs to do is push the partially filled tube upward into the slide until its closure end fits in the seat. A further push moves the tube and slide up and pierces the needle through the closure into the air space in the tube above the liquid therein. Normally this movement of the slide trips a switch that starts the evacuating pump that operates until the desired subatmospheric pressure is established in the tube.